The Evolution of the Mollusks

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  • Topic: Mollusca, Snail, Bivalvia
  • Pages : 2 (536 words )
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  • Published : October 24, 2006
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Snails, clams, squids, chiton. Is it possible that they may all be related in some way? Could they come from the same family tree? How does an octopus related to an oyster other than living in water? Yes it is very true that all of the above named specimen evolved from the same ancestor. The hypothetical ancestral mollusk has evolved into so many different species that are adapted to live in a variety of environments. Among the many species clams and snail, land snails in particular, have evolved in very different ways.

The class of Gastropod is closer to the hypothetical ancestral mollusk than the other classes of mollusks. Gastropods such as snails have a similar body layout that contains the basic broad foot, shell with mantle inside, and mouth with radula present. The class Bivalve, on the other hand, looks to be drastically different in appearance than the Gastropods. Bivalves such as clams have two distinct halves that open and close by muscles. Although they look entirely different they have many of the same physical characteristics. Clams also have a foot present although it is not as broad as that of a snail. Clams have a shell that contains a thin lining inside, which is also known as the mantle. The two species have quite a few things in common based on the hypothetical ancestral mollusk.

The difference comes in largely in the movement of the species and the mouth structure or feeding habits. While a snail has a clear mouth formation complete with a radula, a clam has siphons that obtain food from the water. The siphons are called filter feeders since they "filter" the water. The radula of a snail is used to scrape algae from rocks. Marine snails eat plankton but some are carnivorous and use their radula to drill holes in the shells of other mollusks. Clams move by digging with their "foot" into the sand and burying themselves so that they are camouflaged into the surroundings. The siphons are also used to filter water through in...
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